The invention relates to a radio reception system with at least two different antennas having marked directional effect.
Radio reception systems in which the signals of multiple antennas are implemented in order to improve the reception quality of a receiver are in use in the form of diversity systems, for example.
Diversity systems that are intended for reception of FM radio signals in vehicles, in which multiple antennas are connected with a diversity module on the input side, which module is connected, on the output side, with a receiver, by way of an HF line, whereby a sum signal runs by way of the HF line, consisting of two selected antenna signals, one of which has passed through a phase rotation device, are known from EP 1 763 151 A2, which has a corresponding application published as US2007058761 published on Mar. 15, 2007, the disclosure of which is hereby incorporated herein for reference, for example. There, the diversity module is characterized by two signal paths that have been brought together in a summation element, one of which paths contains the phase rotation device configured as a digitally addressable component, and each of which paths is connected with the antennas on the input side, by means of a signal selection switch that can be addressed by means of a control device. The signal selection switch is set up for producing a connection between the two signal paths with two of the antennas selected from the group of the input-side antennas, as a function of the quality of the sum signal, particularly the occurrence of interference, whereby the discrete phase angles assigned, in fixed manner, to the individual positions of the signal selection switches, are set as a function of the phase value matrix stored in the memory of the control device. The discrete values of the phase rotation angles are selected on the basis of the radiation diagrams of the antennas mounted on the vehicle, with regard to representing maximal diversity efficiency and the smallest possible number of discrete values of the phase angles.
According to this reference, diversity efficiency is understood to mean a parameter that describes the performance capacity of a multi-antenna system, which parameter corresponds to the number of notionally available de-correlated reception signals. At the summation point, it is not an absolutely same-phase setting of the signals to be summed up, but rather a combination that provides a maximal signal/noise ratio that is aimed at.
There is another disclosure, EP 1 126 631 B1, which has a corresponding U.S. patent issued as U.S. Pat. No. 6,925,293 to Lindenmeier et al and which issued on Aug. 2, 2005, which is hereby incorporated herein by reference in its entirety. This patent discloses another diversity system, which differs from the one described above essentially in that a phase rotation device is disposed ahead of a summation point at which the signal paths are brought together, in the course of the one path, which device rectifies the signals to be summed up, to have the same phase. The sum signal that is then formed is subsequently passed to demodulation. The processes of summation of the two signal paths as well as phase rotation in the region of the one signal path are moved into a reception device, and a multi-antenna system that is disposed spatially separate from the reception device is provided with addressable selection switches, by way of which any desired connections between the two signal paths as well as any one of the multiple antennas can be produced. By means of an interference detector that checks the sum signal, the set-up is such that the selection switches are changed to a different constellation of these switches when interference occurs, on the basis of a list of possible switching positions of the selection switches, which list is stored in memory in a logical switching device of the multi-antenna system, in the manner of a matrix, and specifically, this occurs with regulation of the phase rotation device in accordance with a maximal signal/noise ratio.
A characteristic of the nature of these known systems consists in that measures for taking into consideration, i.e. improving the signal/noise ratio are essentially restricted to the selection of antenna signals that are combined at a summation point, with at least approximately the same phase.
Frequently, a semi-spherical radiation characteristic is required for an antenna array that is intended for mobile reception in vehicles, particularly for satellite reception (e.g. Sirius or XM), in which system beam forming, namely orientation toward the satellite, is not provided. However, in comparison with beam forming, this leads to an unavoidable deterioration of the signal/noise ratio. The causes of the interferences that are unavoidably coupled in by way of the antennas are manifold, and these disruptive signal components cannot be eliminated by means of simple amplification, in any case. They always have the effect of reducing the reception quality.
Against this background, it is one of the benefits of the invention to structure a radio reception system of the type indicated initially, in simple manner, with regard to an advantageous signal/noise ratio.